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Hibernate "O-R" Mapping
The document provides an introduction to Object-Relational Mapping (ORM), which is a programming technique to convert data between incompatible type systems in object-oriented languages. It covers the basics of Hibernate mapping, including mapping declarations, attributes, and XML document structures used in ORM. The text also discusses the advantages and disadvantages of using ORM in programming, along with references for further learning.
Hibernate "O-R" Mapping
- 1. Hibernate - ORMapping
- 2. Points to becovered » Introduction to OR mapping » Mapping Declaration »<hibernate-mapping> element » Mapping attributes
- 3. O-R-M Let’s start withthe introduction. 1. Introduction to OR mapping
- 4. Definition » It isa programming technique for converting data between incompatible type systems in object-oriented programming languages. » This creates, in effect, a "virtual object database" that can be used from within the programming language. » Compared to traditional techniques ORM often reduces the amount of code that needs to be written.
- 5. O-R-M Introduction O-R-M stands for“object relation mapping”. Mappings are usually defined in XML document. Mappings are constructed around persistent class declarations
- 6. XML Guide to mapping 2.MappingDeclaration
- 7. Mapping Example Mapping Document <?xmlversion="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="org.somepackage.eg"> <class name="Foo" table=”FooTable”> <id name="id" type=”java.lang.Long”> <generator class=”sequence”/> </id> </class> </hibernate-mapping> 7
- 8. XML Root and attributeof schema 3.<hibernate-mapping> element
- 9. <hibernate-mapping> element <hibernate-mapping schema="schemaName" catalog="catalogName" default-cascade="cascade_style" default- access="field|property|ClassName" default-lazy="true|false" auto-import="true|false" package="package.name" /> Attributesare optional The root element of hibernate mapping document is <hibernate- mapping> element.
- 10. XML Elements & Attributeof <hibernate-mapping> 4.Mapping Attributes
- 11. <class> attributes <class name="ClassName" table="tableName" discriminator- value="discriminator_value" mutable="true|false" schema="owner" polymorphism="implicit|explicit" where="arbitrary sqlwhere condition" persister="PersisterClass" ... /> Attributes are optional The <Class> element maps the domain object with corresponding entity in the database.
- 12. <id> attributes <id name="propertyName" type="typename" column="column_name" unsaved- value="null|undefined|id_value" access="field|property|ClassName" > <generator class="generatorClass"/> /> Attributes areoptional The <id> element defines the mapping from that property to the primary key column.
- 13. <property> attributes <property name="propertyName" column="column_name" type="typename" update="true|false" insert="true|false" formula="arbitrary SQL expression" access="field|property|ClassName" ... />Attributes are optional The <property> element declares a persistent, JavaBean style property of the class.
- 14. <generator> attributes <id name="id"type="long" column="cat_id"> <generator class="org.hibernate.id.TableHiLoGenerator"> <param name="table">uid_table</param> <param name="column">next_hi_value_column</param> </generator> </id> The optional <generator> child element names a Java class used to generate unique identifiers for instances of the persistent class. Attributes are optional
- 15. <many-to-one> attributes <many-to-one name="propertyName" column="column_name" class="ClassName" cascade="cascade_style" fetch="join|select" update="true|false" insert="true|false" ... /> Attributes areoptional An ordinary association to another persistent class is declared using a many-to-one element.
- 16. <one-to-one> attributes <one-to-one name="propertyName" class="ClassName" cascade="cascade_style" constrained="true|false" fetch="join|select" access="field|property|ClassName" /> Attributes areoptional A one-to-one association to another persistent class is declared using a one-to-one element.
- 17. Pros »Portable »Single language »Nesting ofdata »Adding is like modifying »Slow »Tuning »Studying »Complex Queries cons
- 18. “ And I likeasking questions, to keep learning; people with big egos might not want to look unsure.
- 19. » http://www.javatpoint.com/collection-mapping » https://www.tutorialspoint.com/hibernate/hibe rnate_or_mappings.htm »https://en.wikipedia.org/wiki/Object- relational_mapping » http://www.allapplabs.com/hibernate/hibernat e_mapping_in_depth.htm Refrences
- 20.
Editor's Notes
- #5 For example, consider an address book entry that represents a single person along with zero or more phone numbers and zero or more addresses. This could be modeled in an object-oriented implementation by a "Person object" with attributes/fields to hold each data item that the entry comprises: the person's name, a list of phone numbers, and a list of addresses. The list of phone numbers would itself contain "PhoneNumber objects" and so on. The address-book entry is treated as a single object by the programming language (it can be referenced by a single variable containing a pointer to the object, for instance). Various methods can be associated with the object, such as a method to return the preferred phone number, the home address, and so on.
- #10 The root element of hibernate mapping document is <hibernate-mapping> element. This element has several optional attributes. The schema and catalog attributes specify that tables referred to in this mapping belong to the named schema and/or catalog. If specified, tablenames will be qualified by the given schema and catalog names. If missing, tablenames will be unqualified. The default-cascade attribute specifies what cascade style should be assumed for properties and Collections which do not specify a cascade attribute. The auto-import attribute lets us use unqualified class names in the query language, by default.
- #16 An ordinary association to another persistent class is declared using a many-to-one element. The relational model is a many-to-one association: a foreign key in one table is referencing the primary key column(s) of the target table.